1. Field of the Invention
The present invention relates to a push button switch construction, and especially to a push button switch construction for use in thin keyboards.
2. Description of the Prior Art
Keyboards consisting of a plurality of key switches arranged in a matrix are used as data input devices for personal computers and other kinds of electronic equipment. Conventionally, the type of push button switch used for such keyboards has been of the type illustrated by the example shown in FIG. 6 (laid open no. 6-260053 Japan).
The push button switch shown in FIG. 6 consists of a key top 101 with anchor clamps 102 and 103 on its under surface, guide support members 107 and 108, held in place by said anchor clamps 102 and 103, which support the said key top and allow it to freely move up and down, a holder member 125 which is positioned under the key top and has a clamp 127 to support the lower parts of guide support members 107 and 108, and a switching member 135 which performs the switching action as the key top moves up and down.
The said guide support members 107 and 108 are U-shaped, with their respective arms crossing at the center in an X-shape when viewed from the side, and the members rotate freely around the axis formed by this intersection. One end of guide support member 107 is rotatably supported by anchor clamp 102 on the underside of key top 101, while the other end is held by anchor clamp 126 on holder member 125 in such a way as to allow it to freely slide back and forth. One end of guide support member 108 is held by anchor clamp 103 on the underside of key top 101 in such a way as to allow it to freely slide back and forth, while the other end is rotatably supported by clamp 127 on holder member 125.
Normally, the rubber spring forming the switching member 135 pushes up on the intersection of guide support members 107 and 108, thus keeping key top 101 in the raised position and the push button switch in the off condition. From this position, if downward pressure is applied to key top 101, the pantograph type assembly formed by guide support members 107 and 108 folds and allows the key top to be depressed. As the intersecting part of guide support members 107 and 108 is lowered, it flattens the rubber spring of the switching member 135 and places the push button switch in the on condition. When the downward pressure on key top 101 is released, the resilience of the rubber spring causes guide support members 107 and 108 to return to the position shown in FIG. 6, and the switching member 135 returns to the off condition.
In order for guide support members 107 and 108 to move as described above, a U-shaped anchor clamp groove 105 and a U-shaped sliding groove 132 must be incorporated in the underside of key top 101 and the top side of holder member 125 respectively, into which fit anchor pins 115 and 123 on the ends of guide support members 107 and 108, so that these ends can freely slide back and forth. The construction consists of an assembly comprising guide support members 107 and 108 supported by anchor clamp 103 on the underside of key top 101 and anchor clamp 126 on the top side of holder member 125 so that its ends may freely slide back and forth. This construction means that, when assembling the push button switch, whichever side is assembled first, key top 101 or holder member 125, the side to be assembled last cannot be seen during assembly, which makes assembly very difficult. In addition, when such push button switched are made smaller and thinner, the complex shape of the components makes handling very difficult and increases the time required for assembly. Also, because an anchor groove 105 must be incorporated on the underside of key top 101 in order to allow the end of guide support member 108 to slide freely while supporting the key top, it is difficult to mold many pieces at the same time, and so mass production is not efficient and productivity is low. Similarly, the necessity to mold holder member 125 in a shape providing a slide groove 132 on its upper surface requires a complex die and is a drawback.